This project is a long term study of basic control and communication processes in physiological systems. This is pursued through a combination of theoretical and experimental methods utilizing the concepts and techniques of engineering science. The ultimate objective is to describe the dynamic interactive behavior of these complex systems in the form of mathematical models whose parameters are physiologically meaningful. Particular problems under study include the control of pulmonary ventilation in the respiratory system, of cardiac output in the cardiovascular system, of fluid and electrolyte distribution in the renal-body fluid system, of metabolic fuel composition by the endocrine system, and of neuronal network interactions in the nervous system. In all of these studies, use is made of on-line computer control and data processing in animal experiments, and of computer simulation and parameter identification in theoretical studies. Many of these studies have potential clinical usefulness, e.g., for the non-invasive measurement of cardiac output by parameter identification using a mathematical model of the respiratory system, and for the optimization of renal hemodialysis.